Method for producing epoxides by oxidizing olefins

ABSTRACT

The invention relates to a new method for producing epoxides by oxidizing olefins in a homogeneous gas phase reaction, wherein ozone and NO 2  and/or NO are reacted with the desired olefin under mild reaction conditions and without a catalyst. The inventive method can be carried out as a continuous, one-step method in a reactor according to FIG. 1, and requires very little technical input. Monoolefins having 2 to 16 carbon atoms and diolefins having 4 to 16 carbon atoms can be epoxidized.

DESCRIPTION

The invention relates to a new method of producing epoxides viaoxidation of olefins in a homogeneous gas-phase reaction by reactingozone and NO₂ and/or NO with the desired olefin under mild reactionconditions without using a catalyst. The method of the invention can becarried out as a continuous one-step method in a reactor according toFIG. 1, and requires very little technical input. Monoolefins having 2to 16 carbon atoms and diolefins having 4 to 16 carbon atoms can beepoxidized.

Epoxides are important intermediates in the chemical industry and aremainly used in the production of olefin glycols or di-, poly- oroligomers thereof which mostly are processed further to formpolyurethanes. In particular, propylene oxide and ethylene oxide eachare required in amounts of about 5 million tons per year.

Epoxides can be produced from olefins by the chlorohydrin process, byindirect oxidation processes using peroxide reagents, and by catalyticor non-catalytic direct oxidation processes. The oxidations can becarried out in liquid phase or in gaseous phase. Oxidations in liquidphase, which can be carried out either as homogeneous or heterogeneousoxidations, are associated with difficult separation processes andcomplicated technologies. Direct olefin oxidation processes in thegaseous involve relatively long residence times and frequently furnishexcessively low conversion and/or excessively low selectivity withrespect to the epoxide.

Thus, for example, DE 197 54 303 A1 describes a method of producingpropylene oxide from propylene in a homogeneous gas-phase reaction.While this method has a selectivity with respect to propylene oxideof >60%, the propylene conversion is relatively low, being 13% and 15%,respectively. In addition, the method is technically complex and costlybecause the reactor's interior according to this invention is lined withan inert material, particularly with noble metals.

It was the object of the present invention to provide a method ofproducing epoxides by oxidizing olefins, which method requires lowtechnical input, is favorable in cost, and ensures both high selectivitywith respect to the epoxide produced and high conversion of the olefinemployed.

It was found that epoxides can be produced via oxidation of olefins in ahomogeneous, continuous gas-phase process with good yields and goodselectivities with respect to the epoxide produced, by mixing ozone andNO₂ and/or NO, optionally using a carrier gas, passing the resultant gasmixture into a conventional flow reactor, and reacting the correspondingolefin fed with the carrier gas under mild reaction conditions.According to the invention, a pressure of not more than 0.1-1000 mbar,preferably 1-500 mbar, and more preferably 1-200 mbar, is required. Thetemperature required is 50-350° C., preferably 100-300° C., and morepreferably 140-240° C. No catalyst is required in the method accordingto the invention. The residence time in the reaction zone is from 0.1 msto a few seconds at maximum, and is preferably between 0.1 and 300 ms.

Oxygen, as well as inert gases such as helium, argon, nitrogen ormixtures thereof with oxygen can be used as carrier gases.

According to the invention, ozone and NO₂ are employed at a ratio of<0.5. Ozone and NO are preferably employed at a ratio of <1.5.

In a preferred embodiment of the invention, ozone is supplied as anozone/oxygen mixture, preferably 1-15 vol.-% ozone in oxygen, and morepreferably 5-10 vol.-% ozone in oxygen.

The method of the invention is carried out in a conventional flowreactor supplied with said gas mixture of ozone and NO₂ and/or NO andoptional carrier gas. Preferably, the method is performed in a reactoraccording to FIG. 1.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1:

1 Mixing chamber

2 Flow reactor

3 Heatable exterior jacket

In the mixing chamber 1, which is connected with the flow reactor 2,ozone and NO₂ and/or NO, optionally with carrier gas, are mixedtogether. Preferably, this can be done at room temperature. The flowreactor is made of conventional materials stable under the pressureconditions used, and coating thereof with inert materials is notrequired. The results according to the invention are also achieved in aflow reactor made of normal standard steel. Optionally, the flow reactorcan be connected to a GC-MS analyzer and/or a gas flow cell with anFT-IR spectrometer, depending on the intended analysis of the reactiongas.

The method of the invention is universally applicable in that the methodallows for epoxidation of monoolefins having 2 to 16 carbon atoms,preferably up to 5 carbon atoms, most preferably propylene and C₄olefins, and of diolefins having 4 to 16 carbon atoms. The reactoraccording to FIG. 1 can be used with all of the above-mentioned olefins.

Thus, according to the invention, a continuous one-step method isprovided, which requires very little technical input, operates undermild reaction conditions, does not require a catalyst, and exhibits veryshort residence time in the reaction zone, i.e., high throughput. Theselectivity with respect to the epoxide produced is at least 68%, and,in addition, high conversion of at least about 50% is achieved.

With reference to the examples, the invention will be illustrated inmore detail below.

EXAMPLES Example 1

Oxidation of Propylene to Form Propylene Oxide

A flow reactor 2 with a mixing chamber 1 according to FIG. 1 is used,the length of the flow reactor being 60 cm (reaction length: 35 cm) andthe inner diameter 16 mm. The flow reactor is made of quartz and isequipped with a heatable exterior jacket. Helium is used as carrier gasfor the olefin. In the mixing chamber, 11.5 vol.-% of ozone is contactedwith about 23 vol.-% NO₂ and 65.5 vol.-% oxygen. Each of the reactantsis metered in gaseous form via mass flow control systems. No catalyst isused.

a) Reaction is performed at a pressure of 25 mbar and a temperature of180° C.

b) Reaction is performed at a pressure of 10 mbar and a temperature of140° C.

The results of Examples 1a and 1b are summarized in Table 1:

Tem- Resi- pera- dence Propylene Propylene Pressure ture time percentageconversion Selectivity Example [mbar] [° C.] [s] [Vol.-%] [mole-%][mole-%] 1a 25 180 0.25 1.9 49.6 68.9 1b 10 140 0.28 4.0 52.2 81.3 Inthe table: Residence time = residence time of the gas mixture in thereaction zone of the flow reactor Propylene percentage in vol.-% = inthe overall gas flow in the reaction zone Propylene conversion [mole-%]= ratio of reacted moles of propylene and supplied moles of propylene ×100% Selectivity [mole-%] = ratio of moles of propylene oxide formed andreacted moles of propylene × 100%

It was found that, without using a catalyst and in spite of mildreaction conditions, exceedingly short residence time in the reactionzone and thus, high throughput (space-time yield) is possible with themethod according to the invention, the selectivity with respect topropylene oxide being very high.

Example 2

Oxidation of Trans-butylene to Form Cis/Trans-butylene Oxide (Mixture ofIsomers)

Reactions are performed-under the same conditions as in Example 1.

a) Reaction is performed at a pressure of 25 mbar and a temperature of180° C.

b) Reaction is performed at a pressure of 25 mbar and a temperature of230° C.

The results of Examples 2a and 2b are summarized in Table 2:

Tem- pera- Resi- Butylene Butylene Pressure ture dence percentageconversion Selectivity Example [mbar] [° C.] time [s] [Vol.-%] [mole-%][mole-%] 2a 25 180 0.25 1.45 84.3 80.0 2b 25 230 0.23 1.45 53.1 96.9

The denotations in Table 2 correspond to those in Table 1.

Similarly, the results show that high conversion of the employed olefinand high throughput are achieved. The selectivity with respect tocis/trans-butylene oxide is nearly 100%.

Example 3

Oxidation of Isobutylene to Form Isobutylene Oxide

Reaction is performed under conditions as in Example 1, at a pressure of10 mbar and a temperature of 230° C. The reaction length is 12 cm. Theresults are illustrated in Table 3.

Tem- Iso- Iso- pera Resi- butylene butylene Pressure ture dencepercentage conversion Selectivity Example [mbar] [° C.] time [s][Vol.-%] [mole-%] [mole-%] 3 10 230 0.078 3.5 74.9 75.2

High conversion with respect to olefin employed and high selectivity areachieved.

What is claimed is:
 1. A method of preparing an epoxide by oxidation ofan olefin in a homogeneous gas-phase reaction, comprising mixing ozoneand NO₂ and/or NO, feeding the resultant gas mixture into a flowreactor, and reacting the olefin in the flow reactor at a pressure of0.1-1000 mbar and a temperature of 50-350° C.
 2. A method according toclaim 1, wherein the reaction is performed at a temperature of 100-300°C.
 3. A method according to claim 1, wherein the reaction is performedat a pressure of 1-500 mbar.
 4. A method according to claim 1, whereinthe olefin is a monoolefin having 2 to 16 carbon atoms or a diolefinhaving 4 to 16 carbon atoms.
 5. A method according to claim 1, whereinozone and NO₂ and/or NO are mixed in a mixing chamber connected with theflow reactor.
 6. A method according to claim 1, wherein ozone and NO₂and/or NO are mixed with a carrier gas.
 7. A method according to claim1, wherein ozone and NO₂ are in an amount at a ratio smaller than 0.5.8. A method according to claim 1, wherein ozone and NO₂ are in an amountat a ratio smaller than 1.5.
 9. A method according to claim 1, whereinthe flow reactor (2) has a heatable exterior jacket (3) and is connectedwith the flow reactor (2) to a mixing chamber (1), and optionallyconnected to a GC-MS analyzer and/or a gas flow cell with an FT-IRspectrometer.
 10. A method according to claim 1, wherein the reaction isperformed at a temperature of 140-240° C.
 11. A method according toclaim 1, wherein the reaction is performed at a pressure of 1-200 mbar.12. A method according to claim 5, wherein the temperature in the mixingchamber is held at room temperature.
 13. A method according to claim 1,wherein the reaction is performed without a catalyst.
 14. A methodaccording to claim 1, wherein the residence time in the reactor is 0.1to 300 ms.
 15. A method according to claim 6, wherein the carrier gas isoxygen, helium, argon or nitrogen, or a mixture of helium, argon ornitrogen with oxygen.
 16. A method according to claim 1, wherein theozone is supplied in an ozone/oxygen mixture.
 17. A method according toclaim 16, wherein the ozone/oxygen mixture contains 1-15 volume % ozonein oxygen.
 18. A method according to claim 16, wherein the ozone/oxygenmixture contains 5-10 volume % ozone in oxygen.
 19. A method accordingto claim 4, wherein the olefin is a monoolefin having 2 to 5 carbonatoms.
 20. A method according to claim 4, wherein the olefin is amonoolefin having 4 carbon atoms or is propylene.